2.4. Antioxidant activity
2.4.1. Reducing power
Reducing power was determined according to the method
described by Siddhuraju and Becker (Siddhuraju & Becker, 2003).
0.5 mL of sample solution (astaxanthin and astaxanthin/HPCD
inclusion complex, ascorbic acid was employed as a control sample)
at various concentrations were mixed with 2.5 mL of phosphate
buffer (0.2 M, pH 6.6) and 2.5 mL of potassium ferricyanide (1.0%,
w/v). The mixture was incubated at 50 ◦C for 20 min, and then
cooled rapidly. 2.5 mL of trichloroacetic acid (10.0%, w/v) was added
to the mixture, which was then centrifuged at 4000 rpm for 10 min.
2.5 mL of upper layer of the solution was taken out and mixed with
2.5 mL of deionized water and 0.5 mL of ferric chloride (0.1%, w/v),
the mixture was stood for 10 min, then the absorbance was measured
at 700 nm by a 2100 UV–VIS spectroscopy (Unico, Shanghai,
China).